While the use as a cooling and release agent in reusable casting dies is of particular interest in the context of steel casting dies for die casting purposes or forming tools for hot forming purposes, the use as a cooling and lubricating agent is found in the field of machining, for example, in drilling, milling, grinding, cutting, lathing, sawing or thread cutting of cast iron alloys, steel alloys, nickel base alloys, cobalt base alloys, non-ferrous metals and plastic materials, as well as in the field of cold forming.
Such cooling and release agents or cooling and lubricating agents are known from prior art. They serve to cool used casting dies and machined parts. When used as a release agent, a layer is applied at the same time to improve the demolding of the cast product from the die, whereas when used as a lubricating agent, an additional lubrication of the parts and tools is affected that increases their durability.
For example, when casting work pieces on the basis of aluminum, magnesium and zinc or alloys of these metals in a die cast or a squeeze cast method, water-emulsified polymers, such as waxes, silicones or modified polysiloxanes, are used as cooling/release agent. Prior to their use at the die casting tool, the emulsions delivered as a concentrate are diluted to the working concentration required for obtaining a sufficient effect. Typically, dilutions are used that contain 0.12% by weight to 2.5% by weight of dry substance in the cooling and release agent.
The casting die is supplied, for example, under pressure with an alloy melt of 560-740° C. After the solidification of the melt, the cast part is removed from the casting die that is about 450-580° C. hot, and the die is cooled down to about 120-350° C. by spraying a cooling and release agent thereon, it is cleaned if necessary and is again supplied with a melt. The water contained in the cooling and release agent serves to cool the die as well as to free the die from possible residues which, after demolding, remain on the die due to the cooling and release agent used. The release agent is effective in that, depending on the temperature conditions, the polymers themselves form a release layer by being pyrolytically decomposed as the die is filled with the metal to be cast and by subsequent densification.
The use of the known cooling and release agents yields satisfactory results; however, it has some drawbacks.
For example, the cooling and release agent often settles on portions of the die, such as at the die frame and die parting lines, that are not contacted with the metal to be cast and on contours that are less subjected to high temperatures, since the temperature at these portions is insufficient to pyrolytically decompose the cooling/release agent. Instead, the cooling and release agent dries because of the heat still present and can no longer be completely emulsified in water. With repeated spraying operations, this leads to the build-up of a layer resulting in problems of dimensional accuracy of the cast piece and in sealing problems at the die so that casting quality decreases. Insufficient pyrolytic decomposition of the release agent may also cause accretions in the cavity area, which also compromise the casting quality. Residues may be deposited in the surface of the cast piece, for example, in turbulence zones.
The stability and the disposal of these emulsions are also problematic. Longer times of rest after emulsification often result in an inhomogeneous distribution of the active substance in the emulsion, whereby a wetting of surfaces with these cooling and release agents is non-uniform.
The washed-off residues of the known cooling and release agents must also be supplied to a separate waste water treatment since they are not easily biodegradable. Their gaseous residues, which are formed as a result of pyrolytic decomposition during their application, are also hazardous to humans and the environment.
Residues containing wax or silicon often remain on the surface of the cast piece. These are hard to remove so that an increased cleaning effort is required. The removal of these water repellent residues therefore requires the use of strong acids, bases or other solvents.
With known cooling/lubricating agents for machining purposes, the pressure during the chip removal sometimes leads to the forming of built-up edges at the cutting tool and oftentimes causes a bluish discoloration in the machined region of the work piece. The built-up edges reduce the service life of the cutting tool. When the built-up edges become welded on, they can also deteriorate the work piece quality if, for example, parts of the built-up edge come loose and are pressed into the work piece surface. Cooling/lubricating agents moreover sometimes contain mordants as additives that can damage alloy elements in the work piece alloy. The chips produced in machining often have to be freed from cooling/lubricating agents clinging thereto, using multi-stage complex processes, such as filtering and washing, so that the cooling/lubricating agent can be reused in the cycle. The chips themselves often must be disposed of as hazardous waste, since a recycling thereof is not feasible because of the cooling/lubricating agent clinging thereto.